Solving x² + bx + c = 0
The question
(x + 9)(x + 8) = 0
(x + 9)(x + 8) = 0
(x + 9)(x + 8) = 0
(x + 9)(x + 8) = 0
x + 9 = 0orx + 8 = 0
x + 9 = 0→x = −9
x + 8 = 0→x = −8
x = −9orx = −8
- The left side is already a product of two brackets, and the right side is zero. So no factoring is needed.
- If two things multiply to zero, one of them must be zero. So either (x + 9) is zero, or (x + 8) is zero.
- Solve each one. x + 9 = 0 gives x = −9, and x + 8 = 0 gives x = −8. Notice the sign turns over: a + in the bracket gives a negative answer.
- So x = −9 or x = −8. Either one makes the equation true.
How it works.
- 01
The left side is already a product of two brackets, and the right side is zero. So no factoring is needed.
- 02
If two things multiply to zero, one of them must be zero. So either (x + 9) is zero, or (x + 8) is zero.
- 03
Solve each one. x + 9 = 0 gives x = −9, and x + 8 = 0 gives x = −8. Notice the sign turns over: a + in the bracket gives a negative answer.
- 04
So x = −9 or x = −8. Either one makes the equation true.